Optical information recording medium and nickel dithiolate complex compounds employed in the same

ABSTRACT

An optical information recording medium is disclosed, which comprises a substrate and an organic recording layer formed thereon comprising a polymethine dye and a dithiolate transition metal complex compound having formula (I): ##STR1## wherein R 1 , R 2  and R 3  each independently represent hydrogen, a halogen, an alkyl group having 1 to 6 carbon atoms, or a perfluoroalkyl group having 1 to 6 carbon atoms; R 4  and R 5  each independently represent hydrogen, an alkyl group having 1 to 6 carbon atoms, an aryl group or a cyano group, which may form a heterocyclic ring; X represents a cation; M represents a transition metal; n is an integer of 0 to 2, which represents the valence number of the transition metal; and m represents the number of cations, which is an integer of 0 to 2, corresponding to the valence number of the transition metal. Furthermore, novel dithiolate nickel complex compounds for use in the optical information recording medium are disclosed.

This is a division of application Ser. No. 07/420,020, filed on Oct. 11,1989, now U.S. Pat. No. 5,013,634.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical information recording mediumand dithiolate transition metal complex compounds employed in theoptical information recording medium. More specifically, the presentinvention relates to an optical information recording medium capable ofperforming efficient writing operation by laser beams, in particular, bysemiconductor laser beams, and dithiolate transition metal complexcompounds which are effective as a near-infrared-light absorption agentand a light stabilizer for use in the optical information recordingmedium.

2. Discussion of Background

In the field of information recording and reproducing, an informationrecording and reproducing apparatus capable of recording and reproducinginformation by applying a laser beam to a rotating disc-type informationrecording medium is conventionally known. For the above-mentionedinformation recording and reproducing apparatus, there are proposed, forexample, information recording media which comprise a substrate and arecording layer formed thereon, comprising a low-melting metal, or amixture of a low-melting metal and a dielectric material. However, theabove information recording media have the shortcomings of poorpreservability, insufficient resolution, low recording density and highmanufacturing cost.

An information recording medium has been proposed, which is soconstructed that an organic dye-containing thin-film comprising as themain component a polymethine dye, serving as a recording layer, isoverlaid on a substrate. This information recording medium has animproved writing sensitivity and reflectance. Accordingly, it has animproved C/N ratio in reading operation. The above recording medium,however, has the shortcomings of poor stability to light and heat,unsatisfactory preservability and remarkable deterioration of therecording reproduction capability during repeated use.

In order to prevent the deterioration of the recording reproductioncapability in the information recording medium, it is proposed that anickel complex compound be added to the above-mentioned polymethine dyein the composition of the recording layer. However, the recording mediumwhich comprises a recording layer comprising the polymethine dye and theabove-mentioned conventional nickel complex compound is stillunsatisfactory for use in practice because of high pit-error ratio andinsufficient retention of signals for the reproduction of recordedinformation in the course of repeated actual operation.

With the progress of the development of the apparatus such as an opticalrecording medium, an infrared filter, a liquid-crystal display, a laserprinter and various apparatus in the field of electrophotography, aspreviously mentioned, a demand for a dye-containing composition withhigh stability to light, capable of absorbing the light in a region froman infrared region over a near infrared region with high efficiency isrecently increasing.

Conventionally, as a dye for the above-mentioned dye-containingcomposition capable of absorbing the light in the near infrared region,squarium-type dyes, cyanine-type dyes, metal phthalocyanines, platinumbis(dithio-α-diketone) complex compounds, and nickel complex compoundsare known. However, these conventional dyes have their own shortcomings.For example, the squarium-type dyes have the shortcomings that the lightabsorbing intensity is poor, and they cannot be worked into a film; andthe cyanine-type dyes have the shortcomings that they become chemicallyunstable when their molecular chains are elongated to improve the nearinfrared light absording capability. Furthermore, the metalphthalocyanine dyes show such a poor solubility in organic solvents thatthey cannot be worked into a thin film by the solution coating method.In addition, an amorphous film of the metal phthalocyanine dyes iseasily crystallized, so that its application to the optical informationrecording medium is considerably restricted. The platinumbis(dithio-α-diketone) complex compounds have the shortcomings thattheir film-forming properties are poor and chemically unstable.

As for the conventional nickel complex compounds, benzenethiolate-typenickel complex compounds and dithiolene-type nickel complex compoundsare in particular well-known. They cannot satisfy all the requirementssuch as solubility in solvents, compatibility with resins, film-formingproperties and chemical stability.

Among the nickel complex compounds, dithiolate nickel complex compoundshave a distinct property of deactivating oxygen in a singlet state, sothat some attention is paid to the dithiolate nickel complex compoundsas a practical light stabilizer and antioxidant for polyolefins, and asa photo-deterioration preventing agent for the organic dyestuff.However, the solubility in solvents, compatibility with resins andfilm-forming properties of these dithiolate nickel complex compounds areinsufficient for use in practice.

SUMMARY OF THE INVENTION

It is therefore a first object of the present invention to provide anoptical information recording medium which comprises a substrate and arecording layer comprising a polymethine dye, which medium has animproved resistance to light and heat, and excellent preservability forthe repeated information reproduction operation.

A second object of the present invention is to provide a dye-containingcomposition for the optical information recording medium, whichdye-containing composition (i) effectively functions as a near infraredabsorbing agent and a light stabilizer in a recording layer of therecording medium, (ii) is chemically stable, and (iii) has highsolubility in organic solvents and high compatibility with resins, andexcellent film-forming properties.

A third object of the present invention is to provide novel nickelcomplex compounds for use in the optical information recording medium.

The first object of the present invention can be achieved by an opticalinformation recording medium which comprises a substrate and an organicthin-film recording layer formed thereon, which recording layercomprises at least a polymethine dye and a compound having the followingformula (I): ##STR2## wherein R¹, R² and R3 each independently representhydrogen, a halogen atom, an alkyl group having 1 to 6 carbon atoms, aperfluoroalkyl group having 1 to 6 carbon atoms; R⁴ and R⁵ eachindependently represent hydrogen, an alkyl group having 1 to 6 carbonatoms, an aryl group or a cyano group, which may form a heterocyclicring; X represents a cation; M represents a transition metal; n is aninteger of 0 to 2, which represents the valence number of the transitionmetal; and m represents the number of cations, which is an integer of 0to 2, corresponding to the valence number of the transition metal.

The second object of the present invention can be achieved by adye-containing composition for use in the optical information recordingmedium, which dye-containing composition comprises at least onepolymethine dye and a compound having the above-mentioned formula (I).

The third object of the present invention can be achieved by dithiolatenickel complex compounds having formula (II). ##STR3## wherein R⁴ and R⁵are the same as previously defined in formula (I); X represents a cationsuch as cations of quaternary ammonium salts, cations of quaternaryphosphonium salts and a sodium cation; m and n are respectively the sameas defined in formula (I).

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a first embodiment of the opticalinformation recording medium according to the present invention;

FIG. 2 is a cross-sectional view of a second embodiment of the opticalinformation recording medium according to the present invention;

FIG. 3 is a cross-sectional view of a third embodiment of the opticalinformation recording medium according to the present invention;

FIG. 4 is a cross-sectional view of a fourth embodiment of the opticalinformation recording medium according to the present invention; and

FIGS. 5 to 8 are IR spectra of nickel complexes according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an optical information recording medium according to the presentinvention, a recording layer which is formed on a substrate comprises adye-containing composition which comprises a polymethine dye and acompound having formula (I). ##STR4## wherein R¹, R² and R³ eachindependently represent hydrogen, a halogen atom, an alkyl group having1 to 6 carbon atoms or a perfluoroalkyl group having 1 to 6 carbonatoms; R⁴ and R⁵ each independently represent hydrogen, an alkyl grouphaving 1 to 6 carbon atoms, an aryl group or a cyano group, which mayform a heterocyclic ring; X represents a cation; M represents atransition metal; n is an integer of 0 to 2, which represents thevalence number of the transition metal; and m represents the number ofcations, which is an integer of 0 to 2, corresponding to the valencenumber of the transition metal.

Examples of cations represented by X.sup.⊕ in the formula (I) arecations of quaternary ammonium salts, quaternary phosphonium salts andsodium. Examples of transition metals represented by M in formula (I)are nickel, palladium and platinum.

The above-mentioned dithiolate nickel complexes represented by formula(I) for use in the optical information recording medium according to thepresent invention can be generally obtained as follows:

A 3,4-dimercaptopyridine derivative is synthesized from a3,4-dihalopyridine derivative by the same method as employed in thepreparation of dithiol which is disclosed in Japanese Laid-Open PatentApplication 58-105960. The above-mentioned 3,4-dimercaptopyridinederivative is then allowed to react with nickel chloride (NiCl₂),whereby the corresponding dithiolate nickel complex can be obtained.

Examples of 3,4-dihalopyridine derivatives used for the preparation of3,4-dimercaptopyridine derivatives are as follows: ##STR5##

The thus obtained nickel complexes of formula (I) may be nickelcomplexes having a zero valence, and in the presence of a cation such asa tetraalkylammonium salt and a tetraalkylphosphonium salt, monovalentor divalent nickel complexes can be obtained. In such a case, thevalence number of the obtained nickel complexes can be controlled bymeans of a reducing agent such as NaBH₄ and an oxidizing agent such asiodine.

In addition, to make the dithiolate nickel complex unsymmetrical in thestructure, a mixture of the above-mentioned zero-valent nickel complexwhich has a pyridine skeleton and a conventional divalent nickel complexmay be refluxed in an organic solvent under application of heat forexchanging ligands as shown below. Thus, unsymmetrical monovalent nickelcomplexes can be obtained. ##STR6##

Examples of the conventional dithiolate nickel complexes are shown asfollows, but not limited thereto in the present invention. ##STR7##wherein R⁶, R⁷, R⁸ and R⁹ each independently represent hydrogen, analkyl group which may have a substituent, an amino group which may havea substituent, or a halogen atom; and n is an integer of 0 to 2.

                  TABLE 1                                                         ______________________________________                                        Complex No. R.sup.6                                                                              R.sup.7      R.sup.8                                                                            R.sup.9                                  ______________________________________                                        1           Cl     Cl           H    Cl                                       2           Cl     Cl           Cl   Cl                                       3           H      N(CH.sub.3).sub.2                                                                          CH.sub.3                                                                           H                                        4           H      H            H    H                                        5           H      CF.sub.3     H    H                                        6           Cl     H            H    Cl                                       7           H      CH.sub.3     H    H                                        8           H      tert-C.sub.4 H.sub.9                                                                       H    H                                        9           CH.sub.3                                                                             CH.sub.3     CH.sub.3                                                                           CH.sub.3                                 10          H      N(CH.sub.3).sub.2                                                                          H    H                                        11          H      CH.sub.2 OH  H    H                                        ______________________________________                                         Type (2): Diothialate Nickel Complexes No. 12 to No. 17 having formula        (I2).                                                                         ##STR8##                                                                     -   wherein R.sup.10 and R.sup.11 each represent an alkyl group which may      have a substituent, an aryl group which may have a substituent, or a cyano     group; and n is an integer of 0 to 2.

                  TABLE 2                                                         ______________________________________                                        Complex                                                                       No.    R.sup.10         R.sup.11                                              ______________________________________                                        12                                                                                    ##STR9##                                                                                       ##STR10##                                            13                                                                                    ##STR11##                                                                                      ##STR12##                                            14                                                                                    ##STR13##                                                                                      ##STR14##                                            15     CN               CN                                                    16     CH.sub.3         CH.sub.3                                              17     C.sub.2 H.sub.5  C.sub.2 H.sub.5                                       ______________________________________                                         Type (3): Dithiolate Nickel Complexes No. 18 to No. 20 having formula         (I3).                                                                         ##STR15##                                                                    -   wherein R.sup.6, R.sup.7, R.sup.8, R.sup.9 and n are the same as           previously defined.

                  TABLE 3                                                         ______________________________________                                        Complex No.   R.sup.6                                                                             R.sup.7    R.sup.8                                                                           R.sup.9                                    ______________________________________                                        18            H     H          H   H                                          19            H     Cl         Cl  H                                          20            H     Br         H   H                                          ______________________________________                                         Type (4): Dithiolate Nickel Complex No. 21 having formula (I4).               ##STR16##                                                                

In the case where the obtained nickel complex is not divalent, it ispossible to change the above nickel complex into a divalent complex byreduction. More specifically, a dithiolate nickel complex which is notdivalent is dissolved or dispersed in an organic solvent such asmethanol. To this solution or dispersion, a 60% aqueous solution ofsodium hydroxide is added to make the solution or dispersion basic, andNaBH₄ is further added thereto. The mixture is then reduced at about 40°C., whereby the above nickel complex is changed into a divalent complex.

In formula (I), M is not only Ni, but also other transition metals, suchas palladium and platinum. These metal complexes can be obtained in thesame manner as employed in the preparation of nickel complexes.

Among the compounds represented by formula (I), the following dithiolatenickel complex compounds having formula (VI) are novel and preferablefor the dye-containing composition for use in the optical informationrecording medium. ##STR17## wherein R⁴ and R⁵ are the same as previouslydefined in formula (I); X represents a cation such as cations ofquaternary ammonium salts, cations of quaternary phosphonium salts and asodium cation; m and n are respectively the same as defined in formula(I).

The above novel dithiolate nickel complex compounds of formula (II) showa particular absorption intensity in the near infrared region.Furthermore, they can form a hydrogen bonding because of the presence ofa pyridine skeleton therein, which imparts to the above dithiolatenickel complex compounds good properties such as excellent solubility ina polar solvent such as alcohol, excellent compatibility with resins,and high stability. Therefore the above-mentioned dithiolate nickelcomplex compounds according to the present invention are expected to beapplied to the various fields. For instance, the dithiolate nickelcomplex compounds can be used in a safelight filter for photoconductivematerials; a filter which is a barrier to the infrared rays harmful tothe eyes; a plastic film for controlling the growth of plants; a plasticfilm for intercepting heat rays; an infrared rays cut-off filter forsemiconductor receptor elements such as a silicon photodiode; a quencherof oxygen in a singlet state; a fading preventing agent; alight-resistance improving agent for a dye contained in an optical disc;a dye for the recording operation employed in an optical disc; amaterial capable of converting laser beam into heat; an ink compositionfor an ink-jet type printer; an ink composition for a bar coder; aninfrared coupler which forms an infrared absorptive dye for a soundtrack; a filter for an optical converting element; a thermal label forindustrial use; and a solid ink composition contained in an ink ribbonfor thermal image transfer recording.

The nickel complex compounds according to the present invention havingformula (II) has at least one legand of the following skeleton offormula (III): ##STR18##

In the case where the nickel complex of formula (II) according to thepresent invention is unsymmetrical, other conventional legands may beemployed. It is preferable that the nickel complex according to thepresent invention of formula (II) be monovalent. This is because themonovalent nickel complex can exhibit not only excellent solubility in asolvent but also a great absorption intensity in the near infaredregion. To prepare such a monovalent nickel complex, a quaternaryammonium salt and a quaternary phosphonium salt are used as a cationsource.

Examples of the nickel complex compounds of formula (III) according tothe present invention include not only the following zero-valent nickelcomplex compounds, but also the nickel complex compounds which can beobtained by combining the above zero-valent nickel complex compounds andthe cations to be described later. ##STR19##

The above-mentioned nickel complex of formula (II) according to thepresent invention can be obtained as follows:

2,5,6-trichloropyridine-3,4-dithiol is synthesized frompentachloropyridine by the same method as employed in the preparation ofdithiol which is disclosed in Japanese Laid-Open Patent Application58-105960. The above-mentioned 2,5,6-trichloropyridine-3,4-dithiol isallowed to react with nickel chloride (NiCl₂), whereby a symmetricalnickel complex having a zero valence is obtained. When theabove-mentioned reaction is carried out in the presence of a cation, amonovalent nickel complex is obtained. A reducing agent such as NaBH₄may be employed in the course of the reaction, when necessary.Alternatively, the above-mentioned zero-valent nickel complex and adivalent nickel complex may be refluxed in a solvent such as1,2-dichloroethane under application of heat for exchanging legands witheach other. Thus, an unsymmetrical monovalent nickel complex accordingto the present invention can be obtained.

The optical information recording medium according to the presentinvention is basically composed of a substrate and a recording layer.Furthermore, an intermediate layer such as an undercoat layer may beinterposed between the substrate and the recording layer, or aprotective layer may be formed on the recording layer. Alternatively, anair-sandwich type recording medium and a sealed-type recording medium,which will be described later in detail, can be prepared.

When the compound having formula (I) is contained together with apolymethine dye in the recording layer of the optical informationrecording medium according to the present invention, the recordingmedium exhibits an improved resistance to light and heat, andeffectively prevents the deterioration of the recording and reproductioncapability. To enhance the above advantages, the compound of formula (I)may also be contained in the above-mentioned undercoat layer orprotective layer, or in both of them. In this case, it is preferablethat the mixing ratio of the amount of the compound of formula (I) tothe total solid components in the undercoat layer or protective layer bein the range of 2 to 100 wt.%, more preferably in the range of 20 to 100wt.%. If contained in both of the undercoat layer and the protectivelayer, the compound of formula [I) can be added to the composition ofthe respective layers at the above defined mixing ratio.

The preferable properties of the materials for use in the opticalinformation recording medium according to the present invention, and theeach layer will now be explained.

(1) Substrate

When a laser beam is applied to the substrate to perform recording andreproducing operation, the substrate of the optical informationrecording medium is required to be transparent. However, when the laserbeam is applied to the recording layer for recording and reproducingoperation, it is not required that the substrate be transparent.

Examples of the materials for use in the substrate are plastic materialssuch as polyester, acrylic resin, polyamide, polyolefin resin, phenolicresin, epoxy resin and polyimide; glass; ceramic; and finely-dividedmetal particles.

Preformats for address signals and pregrooves may be formed on thesurface of the substrate. The substrate for use in the present inventioncan be manufactured by the conventional photo polymerization method orinjection method.

(2) Recording Layer

Information is recorded in the recording layer by causing some opticalchanges in the layer by exposing the recording layer to laser beams. Therecording layer comprises as the main components a polymethine dye and acompound having formula (I).

Examples of the polymethine dye for use in the present invention arecyanine dyes, merocyanine dyes, and pyrylium dyes.

To improve the recording characteristics and stability, theabove-mentioned polymethine dyes can be used in combination.Alternatively, a mixture of the polymethine dye and other dyes such asphthalocyanine dyes, dioxazine dyes, triphenothiazine dyes, phenanthrenedyes, anthraquinone dyes (indanthrene dyes), xanthene dyes,triphenylmethane dyes and azulene dyes; metals such as In, Sn, Te, Bi,Al, Se, Ag and Cu; and metallic compounds such as TeO₂ and SnO may bedispersed in the recording layer. The above dyes, metals and metalliccompounds may be laminated in the form of a layer on the recording layercomprising the polymethine dye and the compound of formula (I).

The recording layer may further contain a high polymeric substance, astorage stabilizing agent such as metal complexes and phenoliccompounds, a dispersant, a flame retardant, a lubricant, an antistaticagent and a plasticizer.

It is preferable that the mixing ratio by weight of the polymethine dyeto the compound having the formula (I) in the recording layer be in therange of (50 : 50) to (98 : 2), more preferably in the range of (70 :30) to (95 : 5).

The recording layer can be formed on the substrate by the conventionalmethods, such as deposition, sputtering, CVD (chemical vapor deposition)and solution coating. Among the above methods, the solution coatingmethod is preferable. When the solution coating method is employed, thepolymethine dye is dissolved in an organic solvent such as alcohols,ketones, amides, ethers, sulfoxides, esters, aliphatic halogenatedhydrocarbons or aromatic materials, and then the thus obtained solutionis coated on the substrate by the conventional methods such as spraycoating, spinner coating, dip coating, blade coating and roller coating.It is preferable that the thickness of the recording layer for use inthe present invention be in the range of 100 Å to 10 μm, more preferablyin the range of 200 Å to 2 μm.

(3) Undercoat Layer

The undercoat layer is formed for the purposes of (a) improving theadhesion strength between the substrate and the recording layer, (b)preventing the recording layer from being exposed to water and gases,(c) improving the preservability of the recording layer, (d) increasingthe reflectance to the laser beam, (e) protecting the substrate from thesolvent employed and (f) forming the pregroove.

To attain the above-mentioned purpose (a), high polymeric materials suchas ionomer resin, polyamide resin, vinyl resin, natural polymer,silicone and liquid-type rubber; and a silane coupling agent may beused.

To attain the purposes (b) and (c), inorganic compounds such as SiO₂,MgF₂, SiO, TiO₂, ZnO, TiN and SiN; and metals or metalloides such as Zn,Cu, S, Ni, Cr, Ge, Se, Au, Ag and Al can be contained in addition to theabove-mentioned high polymeric materials in this undercoat layer.

To attain the purpose (d), metals such as Ag and Al; and dyes having ametallic luster, such as methine dyes and xanthene dyes may be containedin the undercoat layer.

To attain the purposes (e) and (f), an ultraviolet-curing resin, athermosetting resin and a thermoplastic resin may be used in theundercoat layer.

It is preferable that the thickness of the undercoat layer be in therange of 0.1 μm to 30 μm, more preferably in the range of 0.2 μm to 10μm.

(4) Protective Layer

The protective layer is formed on the recording layer to protect therecording layer from being scratched, and prevent the dust and stainfrom directly adhering to the recording layer. In addition, theprotective layer is also provided to improve the preservability andreflectance of the recording layer.

The same materials as used in the undercoat layer can be employed in theprotective layer.

It is preferable that the thickness of the protective layer be in therange of about 0.05 μm to about 5 μm.

In the undercoat layer and the protective layer, a stabilizer, adispersant, a flame-retardant, a lubricant, an antistatic agent, asurface-active agent and a plasticizer may be contained.

The structure of the optical information recording medium according tothe present invention will now be explained in detail by referring toFIGS. 1 through 4.

As shown in FIG. 1, an optical information recording medium according tothe present invention is basically so costructed that a recording layer2 comprising a polymethine dye and a compound having formula (I) isoverlaid on a substrate 1. In this structure, a two-layered typerecording layer may be employed. For example, a light reflection layerand a light absorption layer may constitute the recording layer. Thelaminating order is not specifically limited in this case.

In FIG. 2, an undercoat layer 3 is interposed between the substrate 1and the recording layer 2.

In FIG. 3, a recording layer 2 and a protective layer 4 are overlaid ona substrate 1 successively, in this order.

In FIG. 4, an undercoat layer 3 is interposed between a substrate 1 anda recording layer 2, and a protective layer 4 is further formed on therecording layer 2.

Furthermore, an optical information recording medium with anair-sandwich structure can be obtained by disposing a pair of opticalinformation recording media selected from the embodiments as shown inFIGS. 1 to 4 in a concentric configuration. Two substrates are sealedvia an air space interposed therebetween, with the respective recordinglayers 2 turned inside. Either of the recording media may have only asubstrate. Alternatively, one optical information recording mediumselected from the embodiments as shown in FIGS. 1 to 4 may be sealedwith the other recording medium with the same structure as the above,with a protective layer 4 interposed therebetween and the respectiverecording layers 2 turned inside, to form an optical informationrecording medium with a sealed-type structure.

Semiconducter laser beams having a wavelength of 750 to 850 nm, servingas a light source for recording and reproducing information, canminimize the size of an optical information recording apparatus.

Other features of this invention will become apparent in the course ofthe following description of exemplary embodiments, which are given forillustration of the invention and are not intended to be limitingthereof.

SYNTHESIS EXAMPLE 1 Preparation of dithiolate nickel complex No. 1according to the present invention{bis(2,5,6-trichloropyridine-3,4-dithiolate)nickel complex}

A mixture of 20 parts by weight of pentachloropyridine, 16 parts byweight of sodium hydrogensulfide (NaHS) with a purity of 70%, 3.4 partsby weight of iron powder, 1.6 parts by weight of sulfur powder and 70parts by weight of N,N-dimethylformamide was heated with stirring in areactor at 130° C. for 10 hours, with a stream of nitrogen gas slowlypassed therethrough. The reaction mixture was cooled, and 200 parts byweight of water was added to this reaction mixture. The resulting blacksolid material was filtered off from the reaction mixture. This blacksolid was air-dried and then mixed with an aqueous solution consistingof 100 parts by weight of methanol, 8 parts by weight of zinc oxide, 20parts by weight of sodium hydroxide and 100 parts by weight of water.This reaction mixture was refluxed under application of heat for 1 hour.After the mixture was cooled, it was filtered. The obtained filtrate waspoured into an acid solution consisting of 200 parts by weight of waterand 100 parts by weight of a 98% sulfuric acid, so that a brown solidmaterial was obtained. The thus obtained brown solid material wasextracted from chloroform. The extract was washed with water severaltimes and the chloroform was removed therefrom by evaporating thechloroform to dryness, whereby 10 parts by weight of2,5,6-trichloropyridine-3,4-dithiol was obtained in the form of a yellowsolid. The melting point was 132 to 133.5° C.

10 parts by weight of the thus obtained2,5,6-trichloropyridine-3,4-dithiol was dissolved in 350 parts by weightof chloroform. To this solution, a solution consisting of 4.8 parts byweight of NiCl₃ ·6H₂ O and 100 parts by weight of ethanol was added, sothat 12 parts by weight of a red zero-valent nickel complex,bis(2,5,6-trichloropyridine-3,4-dithiolate)nickel complex was obtained.The melting point was 300° C. or more. An infrared spectrum of the thusobtained nickel complex, taken by use of a KBr tablet, is shown in FIG.5. In FIG. 5, the mark (*) indicates a peak showing the presence ofwater in the KBr tablet. The thus obtained nickel complex is representedby the following formula: ##STR20##

SYNTHESIS EXAMPLE 2 Preparation of dithiolate nickel complex No. 2according to the present invention{bis(2,5,6-trichloropyridine-3,4-dithiolate)nickeltetra-n-butylammonium}

A mixture of 12 parts by weight ofbis(2,5,6-trichloropyridine-3,4-dithiolate)nickel complex havingzero-valence obtained in Synthesis Example 1 and 10 parts by weight oftetra-n-butylammonium bromide was dissolved in 200 parts by weight of1,2-dichloroethane. This solution was refluxed under application of heatfor 5 hours. The mixture was then cooled and filtered. The thus obtainedfiltrate was evaporated to dryness, so that a green crude product wasobtained. The thus obtained crude product was subjected to columnchromatography, using a silicagel (Trademark "Wakogel C-200" made byWako Pure Chemical Industries, Ltd.) and chloroform as a developingsolvent, whereby 5 parts by weight ofbis(2,5,6-trichloropyridine-3,4-dithiolate)nickel tetra-n-butylammoniumaccording to the present invention was obtained. The melting point was197-199° C.

An infrared spectrum of the thus obtained nickel complex, taken by useof a KBr tablet, as shown in FIG. 6, indicated a maximum absorption at843 nm in a solvent of methanol. The molar absorption coefficient was8900. In FIG. 6, the mark (*) indicates a peak showing the presence ofwater in the KBr tablet. The thus obtained nickel complex is representedby the following formula: ##STR21##

SYNTHESIS EXAMPLE 3 Preparation of dithiolate nickel complex No. 3according to the present invention

A mixture of 10 parts by weight ofbis(2,5,6-trichloropyridine-3,4-dithiolate)nickel complex having azero-valence obtained in Synthesis Example 1 and 15 parts by weight of adivalent nickel complex having the following formula was refluxed underapplication of heat in 520 parts by weight of 1,2-dichloroethane for 5hours: ##STR22##

The mixture was then cooled and filtered. The thus obtained filtrate wasevaporated to dryness, so that a crude product was obtained. The thusobtained crude product was subjected to column chromatography, using amixed solvent of chloroform and 1,2-dichloroethane, serving as adeveloping solvent, whereby 5 parts by weight of dithiolate nickelcomplex compound No. 3 according to the present invention was obtained.The melting point was 127.5-128° C.

An infrared spectrum of the thus obtained nickel complex, taken by useof a KBr tablet, as shown in FIG. 7, indicated a maximum absorption at850 nm in a solvent of methanol. The molar absorption coefficient was9600. In FIG. 7, the mark (*) indicates a peak showing the presence ofwater in the KBr tablet. The thus obtained nickel complex is representedby the following formula: ##STR23##

SYNTHESIS EXAMPLE 4 Preparation of dithiolate nickel complex No. 4according to the present invention

31 parts by weight of a commercially availablebis(3,5,6-trichlorobenzene-1,2-dithiolate)nickel tetra-n-butylammoniumcomplex (Trademark "PA1006" made by Mitsui Toatsu Fine Chemicals Inc.)was dispersed in 270 parts by weight of ethanol. To this dispersion, 12parts by weight of a 50% aqueous solution of sodium hydroxide was addedand 1.5 parts by weight of NaBH₄ was further added. This reactionmixture was stirred at about 40° C. for 2 hours. As a result, thereaction mixture was turned into a red transparent solution.

To the thus obtained red transparent solution, 25.4 parts by weight oftetra-n-butylammonium bromide was added. The mixture was stirred at roomtemperature for 2 hours. A precipitate in the above mixture was filteredoff, washed with water and dried, whereby 36 parts by weight of adivalent bis(3,5,6-trichlorobenzene-1,2-dithiolate)-nickeltetra-n-butylammonium complex was obtained.

A mixture of 5.3 parts by weight ofbis(2,5,6-trichloropyridine-3,4-dithiolate)nickel complex havingzero-valence obtained in Synthesis Example 1 and 10 parts by weight ofthe above prepared divalentbis(3,5,6-trichlorobenzene-1,2-dithiolate)nickel tetra-n-butylammoniumcomplex was refluxed under application of heat in 320 parts by weight of1,2-dichloroethane for 5 hours.

The mixture was then cooled and filtered. The thus obtained filtrate wasevaporated to dryness, so that a crude product was obtained. The thusobtained crude product was subjected to column chromatography, using amixed solvent of chloroform and 1,2-dichloroethane, serving as adeveloping solvent, whereby 6.5 parts by weight of dithiolate nickelcomplex compound No. 4 according to the present invention was obtained.The melting point was 141-142.5° C.

An infrared spectrum of the thus obtained nickel complex, taken by useof a KBr tablet, as shown in FIG. 8, indicates a maximum absorption at860 nm in a solvent of methanol. The molar absorption coefficient was12800. In FIG. 8, the mark (*) indicates a peak showing the presence ofwater in the KBr tablet. The thus obtained nickel complex is representedby the following formula: ##STR24##

EXAMPLE 1

A polycarbonate substrate having a thickness of 1.25 mm and a diameterof 200 mm was prepared, which was provided with grooves having a depthof 950 Å and a half-value width of 0.3 μm, formed by injection moldingat intervals of a track pitch of 1.6 μm in a 45-94 mm radius range ofthe substrate.

A mixture of a dye having the following formula and the dithiolatenickel complex No. 1 obtained in Synthesis Example 1 at a mixing ratioby weight of 85 to 15 was dissolved in a mixed solvent consisting of 80parts by weight of methanol and 20 parts by weight of1,2-dichlorobutane, so that a coating solution for a recording layer wasprepared: ##STR25##

The thus prepared coating solution was coated on the above polycarbonatesubstrate by spin coating, whereby a recording layer having a thicknessof 700 Å was formed on the substrate. Thus, an optical informationrecording medium No. 1 according to the present invention was obtained.

EXAMPLE 2

Example 1 was repeated except that dithiolate nickel complex No. 1employed in the coating solution for the recording layer in Example 1was replaced by dithiolate nickel complex No. 2 obtained in SynthesisExample 2, whereby an optical information recording medium No. 2according to the present invention was obtained.

EXAMPLE 3

Example 1 was repeated except that dithiolate nickel complex No. 1employed in the coating solution for the recording layer in Example 1was replaced by dithiolate nickel complex No. 3 obtained in SynthesisExample 3, whereby an optical information recording medium No. 3according to the present invention was obtained.

EXAMPLE 4

Example 1 was repeated except that dithiolate nickel complex No. 1employed in the coating solution for the recording layer in Example 1was replaced by dithiolate nickel complex No. 4 obtained in SynthesisExample 4, whereby an optical information recording medium No. 4according to the present invention was obtained.

COMPARATIVE EXAMPLE 1

Example 1 was repeated except that dithiolate nickel complex No. 1employed in the coating solution for the recording layer in Example 1was replaced by a commercially available dithiolate nickel complex(Trademark "PA1006" made by Mitsui Toatsu Fine Chemicals Inc.), wherebya comparative optical information recording medium No. 1 was obtained.

COMPARATIVE EXAMPLE 2

Example 1 was repeated except that dithiolate nickel complex No. 1 waseliminated from the coating solution for the recording layer employed inExample 1, whereby a comparative optical information recording mediumNo. 2 was obtained.

EXAMPLE 5

A polymethyl methacrylate substrate having a thickness of 1.2 mm and adiameter of 200 mm was prepared, which was provided with grooves havinga depth of 950 Å and a half-value width of 0.3 μm, formed by use of a 50μm thick photopolymer at intervals of a track pitch of 1.6 μm in a 45-94mm radius range of the substrate.

A mixture of a dye having the following formula and the dithiolatenickel complex No. 2 obtained in Synthesis Example 2 at a mixing ratioby weight of 80 to 20 was dissolved in 1,2-dichloroethane, so that acoating solution for a recording layer was prepared. ##STR26##

The thus prepared coating solution was coated on the substrate by spincoating, whereby a recording layer having a thickness of 700 Å wasformed on the substrate. Thus, an optical information recording mediumNo. 5 according to the present invention was obtained.

EXAMPLE 6

A mixture of a dye having the following formula and the dithiolatenickel complex No. 3 obtained in Synthesis Example 3 at a mixing ratioby weight of 90 to 10 was dissolved in 1,2-dichloroethane, so that acoating solution for a recording layer was prepared. ##STR27##

The thus prepared coating solution was coated on a substrate, which wasprepared by the same procedure as in Example 5, by spin coating, wherebya recording layer having a thickness of 700 Å was formed on thesubstrate. Thus, an optical information recording medium No.6 accordingto the present invention was obtained.

EXAMPLE 7

Example 5 was repeated except that the dye employed in the preparationof the coating solution of the recording layer in Example 5 was replacedby a dye having the following formula, whereby an optical informationrecording medium No. 7 according to the present invention was obtained.##STR28##

EXAMPLE 8

A mixture of a dye having the following formula and the dithiolatenickel complex No. 4 obtained in Synthesis Example 4 at a mixing ratioby weight of 90 to 10 was dissolved in 1,2-dichloroethane, so that acoating solution for a recording layer was prepared. ##STR29##

The thus prepared coating solution was coated on a substrate, which wasprepared by the same procedure as in Example 5, by spin coating, wherebya recording layer having a thickness of 700 Å was formed on thesubstrate. Thus, an optical information recording medium No. 8 accordingto the present invention was obtained.

EXAMPLE 9

A polymethyl methacrylate substrate having a thickness of 1.2 mm and adiameter of 200 mm was prepared, which was provided with grooves havinga depth of 950 Å and a half-value width of 0.3 μm, formed by use of a 50μm thick photopolymer, at intervals of a track pitch of 1.6μm in a 45-94mm radius range of the substrate.

A mixture of a dye having the following formula and the dithiolatenickel complex No.3 obtained in Synthesis Example 3 at a mixing ratio byweight of 90 to 10 was dissolved in 1,2-dichloroethane, so that acoating solution for a recording layer was prepared. ##STR30##

The thus prepared coating solution was coated on the above substrate byspin coating, whereby a recording layer having a thickness of 500 Å wasformed on the substrate.

On the thus obtained recording layer, the following dye was deposited invacuum, so that an overcoat layer having a thickness of 150 Å was formedon the above recording layer. ##STR31##

Thus, an optical information recording medium No. 9 according to thepresent invention was obtained.

COMPARATIVE EXAMPLE 3

Example 6 was repeated except that dithiolate nickel complex No. 3 waseliminated from the coating solution for the recording layer employed inExample 6, whereby a comparative optical information recording mediumNo. 3 was obtained.

COMPARATIVE EXAMPLE 4

Example 8 was repeated except that dithiolate nickel complex No. 4 waseliminated from the coating solution for the recording layer employed inExample 8, whereby a comparative optical information recording mediumNo. 4 was obtained.

COMPARATIVE EXAMPLE 5

Example 6 was repeated except that dithiolate nickel complex No. 3employed in the coating solution for the recording layer in Example 6was replaced by a commercially available dithiolate nickel complex(Trademark "PA1007" made by Mitsui Toatsu Fine Chemicals Inc.) havingthe following formula, whereby a comparative optical informationrecording medium No. 5 was obtained. ##STR32##

A semiconductor laser beam having a wavelength of 790 nm was applied toa substrate side of each of the above-prepared optical informationrecording media No. 1 to No. 9 according to the present invention andcomparative optical information recording media No. 1 to No. 5 at arecording frequency of 0.5 MHz and at a linear speed of 1.5 m/sec inorder to write information therein and to reproduce the recordedinformation therefrom. A reproduction waveform obtained from eachrecording medium was subjected to spectral analysis, using a scanningfilter at a band width of 30 KHz, so that the C/N (Carrier/Noise) ratioof each recording medium was measured.

Furthermore each recording medium was subjected to a forcedreproduction-deterioration test by each of the above-mentioned opticalinformation recording media being illuminated by a tungusten lamp havingan illumination of 54000 lux for 20 hours, and then the reflectance ofeach recording layer of the medium and C/N ratio were respectivelymeasured.

Each of the above-mentioned optical information recording media wassubjected to a forced preservability-deterioration test by allowing eachrecording medium to stand for 1000 hours at 60° C. and 90%RH. Then thereflectance of each recording layer of the medium and the C/N ratio werealso measured.

The results are shown in the following Table 4.

                                      TABLE 4                                     __________________________________________________________________________                     After Forced                                                                            After Forced                                                        Reproduction-                                                                           Preservability-                                           Initial Values                                                                          deterioration Test                                                                      deterioration Test                                        Reflectance                                                                         C/N Reflectance                                                                         C/N Reflectance                                                                         C/N                                                 %     db  %     db  %     db                                           __________________________________________________________________________    Example 1                                                                            20    54  16    48  15    47                                           Example 2                                                                            21    56  18    51  17    52                                           Example 3                                                                            20    56  17    52  18    54                                           Example 4                                                                            20    55  17    50  16    50                                           Example 5                                                                            27    54  22    50  21    50                                           Example 6                                                                            27    55  22    51  20    51                                           Example 7                                                                            26    54  19    50  --    --                                           Example 8                                                                            23    54  19    50  --    --                                           Example 9                                                                            27    55  20    50  --    --                                           Comparative                                                                          20    47  15    41  12    35                                           Example 1                                                                     Comparative                                                                          21    55   7        --    --                                           Example 2                                                                     Comparative                                                                          27    56  10        --    --                                           Example 3                *                                                    Comparative                                                                          27    55  11        --    --                                           Example 4                                                                     Comparative                                                                          26    55  19    47  17    40                                           Example 5                                                                     __________________________________________________________________________     *Unmeasurable                                                            

As apparent from the above tests, the optical information recordingmedia according to the present invention show improved stability to heatand light, and preservability. There is substantially no deteriorationin the recording and reproduction performance of the optical informationrecording media according to the present invention in the course ofrepeated use thereof.

In addition, the optical information recording media according to thepresent invention can record information with high sensitivity and formbits in an appropriate shape when long-wavelength laser beams such as asemiconductor laser beams are employed for writing and reproduction ofinformation.

What is claimed is:
 1. A dithiolate nickel complex compound having theformula (II): ##STR33## wherein R⁴ and R⁵ each independently representhydrogen, an alkyl group having 1 to 6 carbon atoms, an aryl group or acyano group, or R⁴ and R⁵, together with the carbons to which they areattached form a pyridinyl ring; X represents a cation; wherein n and mboth equal
 1. 2. The complex compound of claim 1, wherein said cation isselected from the group consisting of quaternary ammonium salt cations,quaternary phosphonium salt cations and sodium.
 3. The complex compoundof claim 1, wherein said alkyl group is selected from the groupconsisting of methyl, ethyl, propyl and t-butyl.
 4. The complex compoundof claim 1, wherein both R⁴ and R⁵ are cyano.
 5. A dithiolate nickelcomplex compound having the formula (II): ##STR34## wherein R⁴ and R⁵each independently represent hydrogen, an alkyl group having 1 to 6carbon atoms, and aryl group, a cyano group or diemthylaminophenyl,provided at least one of R⁴ and R⁵ is diemthylaminophenyl; X representsa cation; wherein n and m both equal 1.